Various drug carriers (e.g., liposomes, polymers, micro-spheres, antibody-drug conjugates) have been developed to alter the bio-distribution and pharmacokinetic properties of drug molecules. Among such carriers, liposomes offer several advantages as clinical drug delivery vehicles, and at present, there are 13 liposome-mediated drug delivery systems approved for the treatment of a variety of human diseases (e.g., breast cancer, ovarian cancer, meningitis, fungal infections, leukaemia, and others) (Torchilin, Nat. Rev. Drug Discovery, 2005, 4, 145-160). In addition, the liposome mediated delivery of about 30 other small molecule drugs, DNA fragments, and diagnostic compounds are currently at different stages of clinical trials (Felnerova et al., Curr. Opin. Biotechnol, 2004, 15, 518-529). In recent years, liposomes have also been tested as vehicles for gene delivery in approaches for treating human diseases (M. C. de Lima et al., Current Medicinal Chemistry, 2003, 10, 1221-1231; C. Nicolazzi et al., Current Medicinal Chemistry, 2003, 10, 1263-1277; V. Kumar et al., A. Current Medicinal Chemistry, 2003, 10, 1297-1306; S. Li et al., Liposomes: Rational Design; Janoff, A. S. (Ed.), Marcel Dekker, New York, 1999, pp. 89-124).
Many drugs, especially the anti-cancer drugs, cause severe and sometimes life-threatening side effects. Liposomes have been used to reduce these undesirable side effects. Liposomal doxorubicin and other anthracyclin formulations have been approved for clinical use (A. Gabizon et al., Liposomes: Rational Design; Janoff, A. S. (Ed.), Marcel Dekker, New York, 1999, pp. 343-362). These formulations show many advantages, viz., prolonged circulation times, protection of key organs against toxicity, and accumulation of liposome-encapsulated drugs in solid tumors (A. Gabizon et al., Liposomes: Rational Design; Janoff, A. S. (Ed.), Marcel Dekker, New York, 1999, pp. 343-362). In order to achieve selective targeting, recognition moieties are attached to the outer surface of the liposomes. The targeting group can be an antibody, (G. A. Koning et al., Cancer Detection Prevention 2002, 26, 299-307; U. B. Nielson et al., Biochim. Biophys. Acta, 2002, 1591, 109-118; C. Turner et al., S. J. Liposome Res. 2002, 12, 45-50; R. Banerjee, J. Biomaterials Applications, 2001, 16, 3-21)(K. Maruyama et al., Adv. Drug Delivery Rev., 1999, 40, 89-102; N. Oku, Adv. Drug Delivery Rev., 1999, 40, 63-73; D. D. Lasic, Tibtech, 1998, 16, 307-321) a peptide, (L. Zhang, et al., J. Biol. Chem., 2001, 276, 35714-35722; K. Vogel et al., J. Am. Chem. Soc., 1996, 118, 1581-1586) or small molecules, (A. Gabizon et al., S. Adv. Drug. Delv. Rev., 2004, 56, 1177-1192; C. P. Leamon et al., Adv. Drug. Delv. Rev., 2004, 56, 1127-1141) which target specific receptors.
Usually upon targeting, the encapsulated drugs are released passively to the selected tissue sites. This is based on the transport property of the molecules across the lipid bilayers of liposomes. Triggered release of drugs and labeled molecules from liposomes has been recognized to be an attractive therapeutic approach. In this approach of drug delivery, the liposomes, particularly non-polymerizable liposomes, which are most frequently used as the drug delivery vehicles, do not release contents until the membranes are destabilized by the external agents (trigger). The trigger can be a change in pH (M. F. Francis et al., Biomacromolecules, 2001, 2, 741-749; D. C. Drummond et al., Progress Lipid Res., 2000, 39, 409-460; M. J. Turke et al., Biochim. Biophys. Acta., 2002, 1559, 56-68; J. A. Boomer et al., Langmuir, 2003, 19, 6408-6415), mechanical stress (N. Karoonuthaisiri et al., Colloids and Surfaces, B: Biointerfaces, 2003, 27, 365-375; C. Mader et al., Biochim. Biophys. Acta, 1999, 1418, 106-116; V. S. Trubetskoy, J. Controlled Release, 1998, 59, 13-19), metal ions, (S. C. Davis et al., Bioconj. Chem., 1998, 9, 783-792) temperature (S. B. Tiwari, J. Drug Targeting, 2002, 10, 585-591; P. Chandaroy et al., J. Controlled Release, 2001, 76, 27-37; H. Hayashi et al., Bioconj. Chem., 1999, 10, 412-418), light (Z. Li et al., Langmuir, 2003, 19, 6381-6391; Y. Wan et al., J. Am. Chem. Soc., 2002, 124, 5610-5611; C. R. Miller et al., FEBS Letters, 2000, 467, 52-5; M. Babincova et al., J. Magnetism Magnetic Mater., 1999, 194, 163-166), or enzymes such as elastase (P. Meers, Adv. Drug Deliv. Reviews, 2001, 53, 265-272), alkaline phosphatase (L. Zhang et al., J. Biol. Chem., 2001, 276, 35714-35722; K. Vogel et al., J. Am. Chem. Soc., 1996, 118, 1581-1586), trypsin (C. C. Pak et al., Biochim. Biophys. Acta, 1998, 1372, 13-27), and phospholipase A2 (N. Seki, Polym. Bull., 1985, 13, 489-492; S. Takeoka, Macromolecules, 1991, 24, 1279-1283; H. Ringsdorf, Physical Chemistry of Biological Interfaces, Baszkin, A.; Norde, W. (Ed), Marcell Dekker, New York, N.Y., 2000, pp. 243-282; H. Ringsdorf et al., Angew. Chem. Intl. Ed. Engl., 1988, 27, 114-158, L. Hu et al., Biochem. Biophys. Res. Commun., 1998, 141, 973-978; J. Davidsen et al., Int. J. Pharm., 2001, 214, 67-69; J. Davidsen et al., Biochim. Biophys. Acta, 2003, 1609, 95-101). Conformational changes of peptides, induced by the change in pH, have also been used to facilitate the content release from liposomes (M. J. Turke et al., Biochim. Biophys. Acta., 2002, 1559, 56-68; J. A. Boomer et al., Langmuir, 2003, 19, 6408-6415). Two agents (light and enzymes; light and pH change) acting in sequence have been used as the liposomal triggers (O. V. Gerasimov et al., Advanced Drug Delivery Reviews, 1999, 38, 317-338; N. J. Wymer et al., Bioconj. Chem., 1998, 9, 305-308). When the liposomes are conjugated to an antibody (M. F. Francis et al., Biomacromolecules, 2001, 2, 741-749; D. C. Drummond et al., Progress Lipid Res., 2000, 39, 409-460; M. J. Turke et al., Biochim. Biophys. Acta., 2002, 1559, 56-68; J. A. Boomer et al., Langmuir, 2003, 19, 6408-6415) or a suitable ligand (M. J. Turke et al., Biochim. Biophys. Acta., 2002, 1559, 56-68; L. Zhang et al., J. Biol. Chem., 2001, 276, 35714-35722; K. Vogel et al., J. Am. Chem. Soc., 1996, 118, 1581-1586), both active targeting and triggered release can be achieved at the site of choice.
Hybrid liposomes polymerized with domains of non-polymerizable lipids have been used as the carriers when slow and controlled release of the entrapped molecules (dyes) are required (M. A. Markowitz et al., Diagnostic Biosensor Polymers, American Chemical Society, Washington, D.C., 1994, pp. 264-274). In hybrid liposomes, the non-polymerizable lipids phase-separate, during the polymerization process, forming separate lipid domains (N. Seki et al., Polym. Bull., 1985, 13, 489-492; S. Takeoka et al., Macromolecules, 1991, 24, 1279-1283; H. Ringsdorf, Physical Chemistry of Biological Interfaces, Baszkin, A.; Norde, W. (Ed), Marcell Dekker, New York, N.Y., 2000, pp. 243-282; H. Ringsdorf et al., Angew. Chem. Intl. Ed. Engl., 1988, 27, 114-158). The amount of non-polymerizable lipids can be adjusted to control the rate of release of the entrapped molecules (S. Takeoka et al., Macromolecules, 1991, 24, 1279-1283). Hybrid liposomes can be selectively opened at the non-polymerized domains (“uncorking” of the liposomes) using a detergent, a suitable chemical (reducing or oxiding agents) or an enzyme (e.g., PLA2) (H. Ringsdorf, Physical Chemistry of Biological Interfaces, Baszkin, A.; Norde, W. (Ed), Marcell Dekker, New York, N.Y., 2000, pp. 243-282). The resultant liposomes with “holes” retain the spherical structure and rapidly release their contents to the outside media (H. Ringsdorf, Physical Chemistry of Biological Interfaces, Baszkin, A.; Norde, W. (Ed), Marcell Dekker, New York, N.Y., 2000, pp. 243-282).
There are reports in the literature of photo-initiated destabilization of the hybrid liposomes (A. Mueller et al., Macromolecules, 2000, 33, 4799-4804; B. Bondurant et al., J. Am. Chem. Soc., 1998, 120, 13541-13542; D. E. Bennett et al., Biochemistry, 1995, 34, 3102-3113). These liposomes are composed of polymerizable lipids (containing conjugated dienes at the end of the hydrophobic chains) and saturated lipids. The liposomes rapidly release their contents, when exposed to the UV light, during the polymerization process (T. Spratt et al., Biochim. Biophys. Acta, 2003, 1611, 35-43). The literature reports indicate that the hybrid liposomes are either stabilized or destabilized by polymerizations, depending on the structures of the polymerizable lipids (A. Mueller et al., Chem. Rev., 2002, 102, 727-757).
Unpolymerized as well as polymerized liposomes, after intravenous administration, are rapidly recognized by the phagocytic cells of the reticuloendethelial system. As a result, the liposomes are removed from blood stream and accumulate mostly in liver and spleen within a few minutes to a few hours after injection (D. Ppahadjopous et al., Liposomes: Rational Design, Janoff, A. S. (Ed.), Marcel Dekker, New York, 1999, pp. 1-12). In order to promote long circulation times to liposomes, small amounts (<10%) of polymerizable diacyl phosphatidyl inositol has been incorporated into liposomes (D. Ppahadjopous et al., Liposomes: Rational Design, Janoff, A. S. (Ed.), Marcel Dekker, New York, 1999, pp. 1-12). Incorporation of polyethylene glycol conjugated lipids in the liposomes (stealth liposomes) is an alternative strategy to achieve long circulation times (T. Ishida et al., Biosciences Reports, 2002, 22, 197-224; M. C. Woodle, Long circulating liposomes: Old drugs, new therapies, Strom, G. (Ed.); Springer, Berlin, Germany, 1998).
Unpolymerized liposomes are typically not stable in the gastro-intestinal tract; hence, most of the studies on liposomal delivery rely on the intravenous administration of the drug formulations. However, polymerized liposomes maintain their integrity in the GI tract, and a portion of the administered dose (<10%) gets transported into the systemic circulation (J. Rogers et al., Critical Rev. Therapeutic Drug Carrier Sys., 1998, 16, 421-480). Blood vessels of tumors are inherently leaky due to wider inter-endothelial junctions, large number of fenestrae and discontinuous (or absent) basement membranes (H. F. Dvorak et al., Am. J. Pathol., 1988, 133, 95-109). The openings can be up to 400 nm in diameter. Due to such an increase in vascular permeability, liposomes (of diameter 100 nm or less) are known to accumulate in soft or even in solid tumors (K. Maruyama et al., Adv. Drug Delivery Rev., 1999, 40, 89-102; N. Oku, Adv. Drug Delivery Rev., 1999, 40, 63-73; D. D. Lasic, Tibtech, 1998, 16, 307-321).
Of four major classes of ECM degrading enzymes (viz., cysteine proteases, aspartic proteases, serine proteases, and metalloproteases,), matrix metalloproteases (MMPs) have been implicated in several diseases. Based on the structural features (including the amino acid sequences, domain organizations), 26 different types of MMPs have been recognized in human tissues, which fall into six major classes: (i) collagenases, (ii) gelatinases, (iii) stromelysins and stromelysin like MMPs, (iv) matrilysins, (v) membrane type MMPs, and (vi) other MMPs (viz., MMP-20, MMP-23, and MMP-28) (M. Whittaker et al., Chem. Rev., 1999, 99, 2735-2776; G. Murphy et al., Methods Enzymol., 1995, 248, 470-484; R. Kiyama et al., J. Med. Chem., 1999, 42, 1723-1738). Although many of these MMPs have been implicated in different types of human diseases, gelatinase-A (MMP-2) and gelatinase-B (MMP-9) have been widely recognized to be involved in the progression and metastasis in most of the human tumors. Gelatinase-A and -B have been found to be overexpressed in breast tumors (M. Polette et al., Virchows Arch Int. J. Pathol., 1994, 424, 641-645; K. Dalberg et al., World J Surg., 2000, 24, 334-340; R. Hanemaaijer et al., Int J Cancer, 2000, 86, 204-207), colorectal tumors (S. Papadopoulou et al., Tumour Biol., 2001, 22, 383-9; JP Segain et al., J. Cancer Res., 1996, 56, 5506-12), lung tumors, (M. Tokuraku et al., Int J Cancer., 1995, 64, 355-359; H. Nagawa et al., S. Jap. J. Cancer Res., 1994, 85, 934-938), prostate tumors (G. Sehgal et al., Am. J. Pathol., 1998, 152, 591-596), pancreatic tumors (T. Koshiba et al., Surg Today., 1997, 27, 302-304; T M Gress et al., Int J Cancer., 1995, 62, 407-413), and ovarian tumors (T N Young et al., Gynecol Oncol., 1996, 62, 89-99). In fact, the initial discovery of the involvement of MMPs in melanoma cancer and metastasis were ascribed to be due to the overexpression of gelatinase-A and -B (V. Kahari et al., Exp. Dermatol., 1997, 6, 199-213; U. Saarialho-K, Arch. Dermatol., 1998, 294, S47-S54; H. Nagase et al., J. Biol. Chem., 1999, 274, 21491-21494; E. Kerkela et al., Exp. Dermatol., 2003, 12, 109-125; A. R. Nelson et al., J. Clin. Oncol., 2000, 18, 1135-1149; L. A. Liotta et al., Nature, 1980, 284, 67-68).
Aside from the roles of gelatinase-A and -B in tumorigenesis and metastasis in different human tissues, these enzymes have also been found to be involved in other human diseases, such as gouty arthritis (M S Hsieh et al., J Cell Biochem., 2003, 89, 791-799), inflammatory bowel disease (ulcerative colitis) (E. Pirila et al., Dig Dis Sci., 2003, 48, 93-98), abdominal aortic aneurysms (R. Pyo et al., J Clin Invest., 2000, 105, 1641-1649), quiescent Crohn's Disease (A E Kossakowska et al., Ann N Y Acad Sci., 1999, 878, 578-580), glaucoma (C. Kee et al., J Glaucoma., 1999 8, 51-55), and sunlight induced premature skin aging (G J Fisher et al., Curr Opin Rheumatol., 2002, 14, 723-726). Evidently, gelatinase-A and -B exhibit one of the most diverse pathogenic roles, and consequently involved in causing a variety of human diseases, as compared to many other enzymes in the physiological system.